Sputtering apparatus

ABSTRACT

A sputtering apparatus has a chamber for containing an inert gas at low pressure. A bore having metal walls forms part of the chamber. The end of said bore is closed by a cathode which is insulated from the metal walls. A carrier positions objects to be sputtered adjacent an end of the bore remote from the cathode.

Se-n24, 1914 NEE-MAM any 3,838,028-

SPUTTERING APPARATUS Filed Dec. 29, 1972 4 4 Sheets-Sheet 1 l l w I L a fiv- //J/ /7//////// AK/ v .4 v u 'lO f I? J IE I pt. 24, 1974 v. NEEDHAM AL sruurmama APPARATUS EZZZI Patented Sept. 24, 1974 3,838,028 SPUTTERING APPARATUS Victor Needham, Balsall Common, and Maurice Parramore, Birmingham, England, assignors to Lucas Aerospace Limited, Birmingham, England Filed Dec. 29, 1972, Ser. No. 319,390 Claims priority, application Great Britain, Dec. 29, 1971, 60,501/71 Int. Cl. C23c 15/00 US. Cl. 204-298 17 Claims ABSTRACT OF THE DISCLOSURE A sputtering apparatus has a chamber for containing an inert gas at low pressure. A bore having metal walls forms part of the chamber. The end of said bore is closed by a cathode which is insulated from the metal walls. A carrier positions objects to be sputtered adjacent an end of the bore remote from the cathode.

This invention relates to sputtering apparatus for depositing a layer of material on an element, and has as an object to provide a sputtering apparatus in a convenient form.

Accordinng to the invention a sputtering apparatus comprises a chamber for maintaining an inert gas at a low pressure, the walls of said chamber including a metal portion having a substantially cylindrical bore which forms part of the chamber, a cathode arrangement engageable with said metal portion so as to be insulated therefrom and so as sealingly to close an end of said bore remote from the remainder of the chamber, said cathode arrangement including a target surface substantially coaxial with said bore, and means for locating an object to be sputtered within the chamber substantially in alignment with said bore and adjacent the other end thereof, said object forming, in use, part of an anode of the apparatus.

A sputtering device will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic plan view of the apparatus, parts having been removed for clarity,

FIG. 2 is a section on line 22 in FIG. 1,

FIGS. 3 and 4 show diagrammatically, to larger scales, parts of FIG. 2, and

FIG. 5 is a block diagram of a control circuit for the apparatus.

Referring firstly to FIGS. 1 and 2, a chamber has metal walls 11. The chamber 10 includes a generally disc-shaped portion 12 and a peripheral portion 13, to be described later. Extending from the upper wall of the portion 12 are two further chamber portions 14, 15 and a hatch 16, whose locations are shown in outline in FIG. 1. Portions 14, 15 are in part defined by stepped cylindrical bores which open into the chamber portion 12.

Rotatable Within chamber portion 12 is a transport arrangement 17 shown in greater detail in FIG. 3. Arrangement 17 comprises a wheel 18 supported by pillars 19 on a spider plate 20. Wheel 18 is of metal and cast within it are heating elements 21 and cooling pipes 22. Spider plate is sealingly secured to a flanged tube 23 which passes sealingly through the wall 11 at the bottom of chamber portion 12. Conduits 24 communicate with pipes 22 and pass sealingly through tube 23 to make a rotatable connection (not shown) with a source of cooling fluid. Connections with elements 21 are made via slip rings 25 on tube 23. The transport arrangement 17 is rotatable to six discrete locations by means of a Geneva mechanism 26, driven by a motor 27. The wheel 18 has, secured at six equi-spaced locations on its upper face,

strips which define U-shaped recesses 28 adapted to receive and locate square glass substrates 29 upon which sputtering operations are to be performed. The arrangement is such that, in any of the aforesaid six discrete positions of wheel 18, three of the recesses 28 will be aligned with the bores of chamber portions 14, 15 and hatch 16 respectively. Table 18 is electrically connected to the wall 11 of chamber 10.

The chamber 10 communicates with a pump arrangement, shown generally at 30, by means of which chamber 10 can be reduced to a low pressure. The pump arrangement 30 includes a molecular-drag pump, together with a backing pump, the arrangement 30 being capable of reducing the pressure in chamber 10 to a value of 10- Torr.

The arrangement of chamber portion 15 is shown in more detail in FIG. 4, chamber portion 14 being substantially identical. The wall 11 of chamber 10 includes a portion 31 having a stepped cylindrical bore 32 opening into the chamber portion 12. The portion 31 is of metal and is secured to the remainder of wall 11 so as to be in sealing engagement and good electrical contact.

Cathode assemblies 33, 34 are mounted so as sealingly to close the ends of the bores 32 which are remote from chamber portion 12 and respectively define chamber portions 14, 15. FIG. 4 shows, in the interest of clarity, a somewhat exploded View, with cathode assembly 34 lifted away from sealing engagement with wall portion 31. Cathode assembly 34 includes a flanged cylindrical element 35 having an annular channel 36 therein. A lid 37 sealingly engages element 35 and is provided with an inlet 37a and an outlet 38 for cooling fluid. A seal ring 39 of silicon rubber serves to seal cathode assembly 34 to wall portion 31 and also to ensure that portion 31 and cathode assembly are mutually insulated electrically.

The cylindrical element 35 includes a circular plate 40 which provides the sputterting target and which is formed of the metal to be sputtered on to a workpiece positioned in a recess 28 below the cathode assembly 34 on the wheel 18. The plate 40 is secured by soldering to the remainder of element 35, which can be made of any con venient metal. An electrical terminal 41 is secured to the element 35.

The axial lengths of the cathode assembly 34 and the stepped portion 42 of bore 32 are such that plate 40 does not extend below the stepped portion 42. A radial clearance 43 exists between the cylindrical portion of element 35 and stepped bore portion 42.

An annular gallery 44 extends around bore portion 42 within wall 31 and communicates with the bore by means of radial holes 45. A conduit 46 connects gallery 44 with a source of inert gas, as for example argon. A pressure sensing device 47 communicates with the chamber portion 15. A vehicle ignition plug 48 is modified by removal of its earth electrode and by removal of part of its threaded case adjacent the HT. electrode. Plug 48 is sealingly mounted in wall portion 31 so that the HT. electrode of the plug is directed towards chamber portion 15. An aperture plate 49 extends across the end of bore 32 remote from the cathode assembly 34 and defines a window through which material can be sputtered on to the workpiece.

In the example described plate 48 consists of gold, and the corresponding plate in cathode assembly 33 is of a nickel-chrome alloys.

The chamber portion 16 has no associated cathode assembly, but has instead an access cover (not shown) sealingly engageable with the wall of portion 16. The workpieces may thereby be removed from the apparatus via chamber portion 16 after sputtering.

Chamber portion 13 (FIGS. 1 and 2) includes a magazine 51) into which five glass substrates can be loaded. A

cathode assembly 51 is substantially the same as cathode assembly 34, described above. Cathode assembly 51 has, however, no plate corresponding to the plate 40. Assembly 51 is, moreover, mounted in the base of chamber portion 13 so as to lie substantially flush with the bottom wall thereof.

A rack and pinion transfer arm 52 is operable to move the substrates sequentially from the magazine 50 on to the centre of the cathode assembly 51. A further rack and pinion transfer arm 53 is operable to move individual substrates from cathode assembly 51 into an adjacent location on the wheel 18, via a passage 54 interconnecting chamber portions 12, 13.

The wall 11 of the chamber and the wheel 18 are both connected to earth. Connected between the terminal 41 and the wall 11, via a control and switching unit 55 (FIG. is an alternating voltage. The frequency of this voltage is 13.5 mHz., and the voltage applied can be raised to 2.5 kv. The corresponding terminals of cathode assemblies 33, 51 are similarly connected to an alternating voltage.

The wall 11 of chamber together with the table 18, forms the anode of the apparatus. The effective area of the anode is thus very much greater than that of any of the cathodes. Application of an R.F. potential to any one of the cathodes results in a D.C. bias potential, relative to earth, at the cathode once a plasma has been established. This bias potential ensures that material is ejected from the cathode only. The bias potential is detected by a D.C. meter 56 (FIG. 5) and is also supplied via a filter circuit 57 to one input of a differential amplifier 58. The other input of amplifier 58 is supplied with a reference voltage from a source 59.

An output signal from amplifier 58 provides a control signal for the control unit 55, which in use, is responsive to amplifier 58 to vary the R.F. potential so as to maintain the D.C. bias substantially constant. An output signal from amplifier 58 also indicates the presence of a plasma between the cathode and anode, and operates a relay 60. The relay 60 in turn controls a timer 61, by means of which the length of a sputtering operation may be set. At the end of a preset time timer 61 causes control unit 55 to switch off the R.F. supply to the cathode.

Uniformity of deposition and the adhesion of a sputtered layer are improved by reducing the pressure within a sputtering chamber. It is not, however, possible to initiate a plasma field at the ideal sputtering pressures by means of the R.F. voltage alone. It has been found, however, that a plasma can be initiated, at the lowest pressures at which the plasma can be maintained, by means of spark plug 48, whose H.T. electrode is supplied with kv. from a conventional spark generator 62, via a switch 63. Switch 63 is itself under the control of relay 60, whereby the supply to the plug 48 is switched off when the plasma has been initiated.

If the plasma should inadvertently become extinguished the relay 60 stops the timer 61 and causes the plug 48 to be energised to re-establish the plasma. If this is successful, the sputtering operation restarts and continues to the end of the period set by the timer 61. If the plasma cannot, however, be re-established, an integrating timer 64, responsive to the duration of operation of the plug 48, operates an alarm 65 and switches off the R.F. supply.

A further timer 66 is responsive to the time over which the plasma remains in being and, in the absence of the plasma for a predetermined period, will also operate the alarm 65 and switch off the R.F. supply.

In use, five substrates are loaded into the magazine 50, these substrates having first been cleaned to remove gross contamination. The substrates are sequentially loaded on to cathode 51 where they are subjected to a sputter-etching operation which removes all traces of contamination. After etching each substrate is transferred by arm 53 on to the wheel 18, five of the six locations on the Wheel 18 thus being occupied at the end of the cleaning and transfer operation.

The wheel is indexed until the vacant location is aligned with cathode assembly 33. The wheel 18, and consequently the substrates, are heated to a temperature of 300 C. The R.F. supply is switched on to cathode assembly 33 and the plasma established by means of the associated spark plug. This operation serves to clean the target surface of cathode assembly 33 and is the reason for the vacant location on wheel 18. After cleaning cathode 33 the wheel is again indexed to bring the first substrate into alignment with cathode 33 and nickel-chrome alloy is sputtered on to the substrate. The sputtering operation is repeated for the remaining four substrates, after which the vacant location is aligned with cathode assembly 34. The wheel 18 and the substrates are cooled to a temperature of C. to 200 C. and the sputter cleaning process is carried out on cathode 34. The substrates are then successively sputtered with gold. Finally the substrates are cooled to room temperature and removed via the hatch 16.

During both the sputter-etching and sputter-deposition operations a supply of argon gas enters the chamber 10 via the gallery, corresponding to gallery 44, of the cathode assembly which is in use. This results in an even distribution of argon within the cathode assembly of deposition. found significantly to improve the uniformity of deposition. Moreover ensuring that all electrically earthed material in the vicinitiy of the cathode is symmetrical with the cathode has also been found to assist in obtaining uniformity of deposition during sputtering.

The radial dimension of the gap 43 around each cathode assembly is less than that of the dark space adjacent the cathode. There is thus no ion bombardment of any part of the chamber portion. The walls of the chamber thus provide dark-space shielding for the cathode.

The use of dark space" shielding, and of control of deposition by timing of plasma duration eliminates the requirement for movable shields within the chamber. Since, in a cycle involving a batch of five substrates, all cleaning, sputtering and transfer processes are performed under the control of electrical signals, the timing and sequence of these processes may readily be controlled by a punched card or a perforated or magnetic tape.

What is claimed is:

1. A sputtering apparatus comprising a chamber for maintaining an inert gas at a low pressure, the walls of said chamber including a metal portion having a substantially cylindrical bore which forms part of the chamber, a cathode arrangement engaged with said metal portion so as to be insulated therefrom and so as sealingly to close an end of said bore remote from the remainder of the chamber, said cathode arrangement including a target surface substantially coaxial with said bore, and means for locating an object to be sputtered within the chamber substantially in alignment with said bore and adjacent the other end thereof, said object forming, in use, part of an anode of the apparatus.

2. A sputtering apparatus as claimed in Claim 1 in which said locating means is of metal and is electrically connected to said metal wall portion, said wall portion, said locating means and said object being, in use, at the same electrical potential.

3. A sputtering apparatus as claimed in Claim 2 in which said bore comprises first and second axially aligned portions, said second portion having a lesser diameter than said first portion, said first portion communicating at one end thereof with the remainder of said chamber and said second portion communicating with an end of said first portion remote from said one end thereof.

4. A sputtering apparatus as claimed in Claim 3 in which said cathode arrangement includes a substantially cylindrical portion which extends with radial clearance into said further bore.

5. A sputtering apparatus as claimed in Claim 4 in which the free end of said cylindrical portion lies within said further bore.

6. A sputtering apparatus as claimed in claim 1 which includes a further electrode extending sealingly into said chamber, and means for supplying a voltage to said further electrode to initiate the establishment of a plasma in said chamber.

7. A sputtering apparatus as claimed in Claim 6 which includes means for applying an alternating voltage between said cathode arrangement and said anode.

8. A sputtering apparatus as claimed in Claim 7 which includes means for detecting a D.C. potential at said cathode arrangement, and a comparator for providing a first electrical control signal dependent on the difierence between said D.C. potential and a reference voltage, said alternating voltage applying means being responsive to said first electrical control signal to vary said alternating voltage so as to maintain said D.C. potential substantially constant.

9. A sputtering apparatus as claimed in Claim 8 which includes means operable in response to the establishment of a plasma in said chamber to provide a second electrical signal, and a timer responsive to said second electrical signal to provide a third electrical signal which is dependent on the desired duration of a sputtering operation, said alternating voltage applying means being responsive to said third electrical signal.

10. A sputtering apparatus as claimed in Claim 1 in. which said locating means includes a table rotatably mounted in said chamber and provided with a plurality of recesses for receiving objects to be sputtered, and means for indexing said table so as successively to align said recesses with said bore.

11. A sputtering apparatus as claimed in Claim 10 which includes a plurality of metal wall portions defining respective bores, and a plurality of cathode arrangements respectively engageable with said wall portions, said recesses being equispaced about the axis of rotation of said table, and said metal wall portions being located relative to the remainder of said chamber so that objects located, in use, in said recesses are successively aligned with the bores in said respective metal portions as said table is indexed.

12. A sputtering apparatus as claimed in Claim 11 in which the cathode arrangements include target plates, adjacent cathode arrangements having target plates of different metals.

13. A sputtering apparatus as claimed in Claim 1 which includes means for successively loading a plurality of said objects on to said locating means.

objects sequentially from said magazine to said locating means.

15. A sputtering apparatus as claimed in Claim 14 in which said loading means includes a further cathode arrangement upon which each said object is located by said transfer means during movement from said magazine to said locating means.

16. A sputtering apparatus as claimed in Claim 1 which includes an aperture plate extending across the first-mentioned bore at the end thereof adjacent the remainder of said chamber, said aperture plate defining a window which overlies an object positioned by said locating means in alignment with said bore.

17. A sputtering apparatus as claimed in Claim 1 which includes an annular passage in said chamber wall surrounding said cathode arrangement, and means for introducing said inert gas into said passage, said passage communicating with said chamber so as to permit said gas to be supplied to said chamber with substantially even distribution around the axis of said cathode arrangement.

uum, vol. 17, No. 3, March 1967, p. 142.

JOHN H. MACK, Primary Examiner W. A. LANGEL, Assistant Examiner US. Cl. X.R. 204--192 

